The present invention relates to a process for the electroless deposition of copper coatings on iron and iron alloy surfaces by means of solutions containing copper and hydrogen ions, and to a solid concentrate for carrying out this process.
It is known to facilitate the cold forming of iron and iron alloys by applying a copper coating onto the workpiece to be formed. Such coatings can be generated in an electroless way in that the metal surface is brought in contact with an aqueous, acid solution containing copper ions. In order to achieve good and in particular adhesive coatings, numerous proposals have been made, which provide for the addition of a variety of modifiers.
In the process in accordance with the DE-C-714 437 copper plating solutions are being used, which in addition to copper, hydrogen, chloride, bromide and/or fluoride ions contain strong organic pickling inhibitors for delaying the dissolution of iron. Useful pickling inhibitors include for instance coal tar bases, the bases extracted from animal distillates, aldehyde amine reaction products, aldehyde ketone reaction products, numerous amino acids, alkaloids and the sulfonated derivatives thereof.
Furthermore, it is known to add polyhydroxy thiols (U.S. Pat. No. 2,410,844) and brightening agents or grain refining agents, such as condensation products of fatty alcohols, fatty acids, tall oil, alkyl phenols, fatty amines, substituted thioureas, each comprising ethylene oxide, as well as long-chain organic amines, reducing sugars, and decomposition products of sugar (FR-A-1,257,758) to electroless copper plating solutions.
It is also known to provide a treatment with an aqueous, acid solution containing copper ions, chloride ions and an organic modifier for the electroless production of copper coatings on iron and iron alloys, where acridine and/or acridine derivatives are used as an organic modifier (DE-B-16 21 291).
Finally, it is known to use solutions containing copper, hydrogen and fluoride ions for the electroless deposition of copper, for which solutions both the fluoride concentration and the hydrogen ion concentration are chosen within certain coordinates in dependence on the temperature (DE-B-16 21 293).
Despite the multitude of known processes for the electroless deposition of copper, problems repeatedly arise in practice, as one does not, or not with the required safety, succeed in producing copper coatings which are both bright and adhesive, cover uniformly, and have a good appearance. A further problem is that the solid concentrates normally used for making the copper plating solutions have a poor flowability and are thus difficult to handle.
It is the object of the invention to provide a process for the electroless deposition of copper coatings on iron and iron alloy surfaces, which does not have the known, in particular the aforementioned disadvantages, and is able to produce uniform and adhesive coatings.